1. Field of the Invention
The present invention relates to a QFN semiconductor package and more particularly to a super thin quad flat non-leaded semiconductor package without die pad.
2. Description of the Prior Art
According to shape of the outer lead, there are three types of Quad Flat Package (QFP), known as Quad Flat I-leaded (QFI) type, Quad Flat J-leaded (QFJ) type, and Quad Flat Non-leaded (QFN) type. With hidden lead and tightly sticking to circuit board during bonding, QFN package accords with the demand of being light, thin and compact for modern electricity components, especially components used in mobile electronics, such as cellular phone or notebook computer, etc.
FIG. 1 shows a sectional view of a generally known QFN package 100; the die 110 is supported by conductive die pad 150 beneath. There are inner leads 120 around the die 110. In order to minimize the height difference and to shorten the distance between inner leads 120 and bonding pad of die 110, each inner lead 120 has a front protruding end with a higher position extended close to die 110 used for conductive wire bonding for electrical connection between the die 110 and the inner lead 120. A drawback is that the front protruding end of the inner lead 120 is hard to be stabilized or supported and then is easy to be forced to bend while wire-bonding. Another drawback is that QFN package 100 gains a thicker thickness due to using the die pad 150 to support the die 110.
A generally known QFN package had been disclosed in U.S. Pat. No. 5,942,794, which has a similar structure as QFN package 100 mentioned in previous, except for using tie bar curving upward on the four corners to support a die pad which forms a higher set area for placing a die, so that the resin can seal the die and bottom of the die pad. Though this structure prevents from the interference between semiconductor die and inner leads, yet it also gains thicker thickness of the package. Because of the inner lead sticking on bottom of the package, there is a height difference and longer distance between the inner lead and the bonding pad of the die, thus a longer bonding wire to electrically connect die and inner lead is necessary. Besides, due to exposing too much surface of the inner lead outside resin encapsulate, it is easy to fall off after encapsulating.
In U.S. Pat. No. 5,986,334, there is another QFN package with better stability for lead frame and die. By using a pre-molding package body to support the die and inner lead, the die and the inner lead get better reliability during wire-bonding and after encapsulating; but the QFN package with a pre-molding body still has a considerable thickness and the producing process of the package becomes more complex in order to produce a special shape of pre-molding package body.
Therefore it is the first object of the invention to provide a QFN package in which use of the middle part of the inner lead protrudes from both ends of the inner lead so that the inner lead of the thinner QFN package has a strong holding.
It is the second object of the invention to provide a QFN package in which use of the middle part of the inner lead protrudes from both ends of the inner lead and some upper side of the middle part is exposed outside from the molding compound so that the upper face and lower face of the package are used for the outer electrical connection of the package resulting in becoming a stackable QFN package.
It is the third object of the invention to provide a lead frame of QFN package in which use of each inner lead of the lead frame is divided into a front finger portion, a middle protruding portion and a rear connecting portion and furthermore the middle protruding portion has a higher height than the front finger portion and the rear connecting portion so that the lead frame of QFN package is easy to be held in a QFN package.
In accordance with one aspect of the invention, a QFN semiconductor package comprises a die having a upward topside and the topside of die having a plurality of bonding pads; a lead frame consisting of a plurality of inner leads around the die, wherein each- inner lead is divided into a front finger portion, a middle protruding portion, and a rear connecting portion, the front finger portion being configured for the bonding of a bonding wire, the rear connecting portion being configured for the outer electrical connection of the QFN package, the middle protruding portion having a higher height than the front finger portion and the rear connecting portion; bonding wires being bonded to connect the bonding pads of the die and the front finger portions of the inner leads; and a molding compound at least sealing the bonding wires and at least exposing the downside of the die and some surfaces of the rear connecting portions of the inner leads. Thereby, the inner leads of the QFN package have a better holding after encapsulating and a stronger support during wire-bonding.
Further, in accordance with another aspect of the present invention, the inner lead of the QFN package has a middle protruding portion which height is equal to the maximum height of the QFN package resulting in the some upper face of the middle protruding portion exposed to outer of the molding compound for another outer electrical connection of the QFN package. It combines with the some lower face of the rear connecting portion exposed to outer of the molding compound for general outer electrical connection of the QFN package so that the QFN package becomes a stackable package device.